Stellar Evolution: Stellar Evolution:

The Life Cycle of a StarThe Life Cycle of a Star

Stellar NurseriesStellar Nurseries

All stars start out in a nebula (large cloud All stars start out in a nebula (large cloud of dust and gas).of dust and gas).

The main element in this cloud is The main element in this cloud is hydrogen.hydrogen.

The particles of material in a nebula have The particles of material in a nebula have a very weak a very weak gravitationalgravitational attraction for one attraction for one another. another.

A force, such as the A force, such as the explosion explosion of a nearby of a nearby star or star or collisioncollision with another nebula, with another nebula, compressescompresses some of the particles. some of the particles.

Stellar NurseriesStellar Nurseries

These particles begin to These particles begin to contractcontract. . As more and more particles come As more and more particles come

together, they begin to together, they begin to spinspin. . This This shrinking, spinningshrinking, spinning region flattens into region flattens into

a a disdisk, with a central concentration of k, with a central concentration of matter known as a matter known as a protostar.protostar.

This protostar will continue to contract and This protostar will continue to contract and heat up for billions of years. Eventually heat up for billions of years. Eventually the gas is so hot that it becomes the gas is so hot that it becomes plasmaplasma. .

A Look in the Cradle: A Look in the Cradle: The Orion NebulaThe Orion Nebula

It spans 40 light years across.It spans 40 light years across. It’s about 1500 ly away.It’s about 1500 ly away. It’s located in the same spiral arm of our It’s located in the same spiral arm of our

galaxy as our sun.galaxy as our sun.Notice the hot, blue regions of star Notice the hot, blue regions of star

formation.formation.

A Star becomes a StarA Star becomes a Star

Once it reaches 10,000,000 C, Once it reaches 10,000,000 C, nuclear nuclear fusionfusion begins and it is officially a star. begins and it is officially a star.

Here, Here, hydrogen hydrogen atoms are fused into atoms are fused into heliumhelium atoms. atoms.

Main SequenceMain Sequence

After the nebula to protostar to star After the nebula to protostar to star phase, the star is at a phase, the star is at a stablestable time of its time of its life known as life known as main sequencemain sequence. .

Here Here gas pressuregas pressure from inside from inside balances balances out the intense pull of out the intense pull of gravitygravity pulling pulling matter in. matter in.

The star stays relatively the same size The star stays relatively the same size and temperature. and temperature.

It will spend nearly 90% of its life here. It will spend nearly 90% of its life here.

The “Golden” YearsThe “Golden” Years

Toward the end of this phase, it begins to Toward the end of this phase, it begins to run out of run out of hydrogenhydrogen and begins to fuse and begins to fuse heliumhelium into into carboncarbon in its in its corecore. .

At the same time, its outer shell expands. At the same time, its outer shell expands. The size of the star begins to matter now. The size of the star begins to matter now. The original The original massmass of the star determines of the star determines

what steps it will go through at the end of what steps it will go through at the end of its life cycle.its life cycle.

Low Mass StarsLow Mass Stars

A A low masslow mass star will become a star will become a giantgiant, , approximately 10 or more times larger approximately 10 or more times larger than our sun. than our sun.

The giant will shed its outer core as a The giant will shed its outer core as a planetary nebulaplanetary nebula. .

The last of its matter gets squeezed The last of its matter gets squeezed together in the form of a together in the form of a white dwarfwhite dwarf. .

When this white dwarf no longer emits When this white dwarf no longer emits energyenergy, it may become a dead star, also , it may become a dead star, also known as a known as a black dwarf.black dwarf.

NGC 2266: Notice the red giantsNGC 2266: Notice the red giants

This is the Helix Nebula – another This is the Helix Nebula – another planetary nebula, with a white planetary nebula, with a white

dwarf in the middledwarf in the middle

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What will happen to our sun?

In 1764, Charles Messier was compiling a list of "annoying" diffuse objects not to be confused with "interesting" comets. The 27th object on Messier’s list, now known as M27 or the Dumbbell Nebula, is a planetary nebula, the type of nebula our Sun will produce when nuclear fusion stops in its core. M27 is one of the brightest planetary nebula in the sky. It takes light about 1000 years to reach us from M27, outer-envelope, leaving an X-ray hot white dwarf, much like the one our sun will form.

Notice the white dwarf star in the middle!!!

NGC6369 – Little Ghost Nebula

CAT’S EYE NEBULA

Three thousand light-years away, a dying star throws off shells of glowing gas. This is the Cat’s Eye Nebular, though to be one of the most complex planetary nebulae known. In fact, the features seen in the Cat’s Eye are so complex that astronomers suspect the bright central object may actually be a binary star system.

High Mass StarsHigh Mass Stars

A A high masshigh mass star will become a star will become a supergiantsupergiant, , approximately 100 times bigger than our sun. approximately 100 times bigger than our sun.

At the end of the supergiant phase, the star will At the end of the supergiant phase, the star will fuse atoms to form heavier elements such as fuse atoms to form heavier elements such as iron iron or even or even goldgold. .

FusionFusion continues until the continues until the corecore is almost entirely is almost entirely iron.iron.

The star will then explode as The star will then explode as a supernova.a supernova.

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Orion, the Hunter, is one of the most easily recognizable constellations. Cool red giant Betelgeuse takes on a yellowish tint as the brightest star at the upper left. Orion's hot blue stars are numerous, with supergiant Rigel balancing Betelgeuse at the lower right, Bellatrixat the upper right, and Saiph at the lower left. And if the middle "star" of Orion's sword looks reddish and fuzzy to you, it should. It's the stellar nursery known as the Great Nebula of Orion.

THE VEIL NEBULA

These wisps of gas are all that remain visible of a Milky Way star. Many thousands of years ago that star exploded in a supernova leaving the Veil Nebula. At the time, the expanding cloud was likely as bright as a crescent Moon toward the constellation Cygnus, visible for weeks to people living at the dawn of recorded history.

High Mass StarsHigh Mass Stars

It may then become a It may then become a neutron starneutron star, with , with gravity gravity so intense that it combines so intense that it combines protonsprotons and and electronselectrons into into neutronsneutrons. .

A spoonful of matter from a neutron star A spoonful of matter from a neutron star would weigh 100 million tons on Earth! would weigh 100 million tons on Earth!

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The Crab Nebula is the result of a star that was seen to explode in 1054 AD. This spectacular supernova explosion was recorded by Chinese and Native American astronomers. In the nebula's very center lies a pulsar: a neutron star rotating, in this case, 30 times a second.

High Mass StarsHigh Mass Stars

However, the However, the most massive starsmost massive stars will not will not become neutron stars. become neutron stars.

They will, instead, They will, instead, contract contract even further even further into a into a black holeblack hole, where gravity is so , where gravity is so strong that not even strong that not even lightlight can escape. can escape.